1) Field of the Invention
This invention relates to a rolling bearing, and especially to a rolling bearing effectively usable under such usage conditions that a housing with the rolling bearing held thereon is elastically deformed by external force and off-load is applied to the bearing due to the resulting deformation or in such a field that the bearing is used at high temperature and high speed and under heavy load.
2) Description of the Related Art
In the case of a rolling bearing employed, for example, in an alternator of an automobile, its outer race is prone to damage, primarily flaking and the like because its aluminum-made housing undergoes elastic deformation due to external force and off-load is hence applied. In the case of a rolling bearing employed in an electromagnetic clutch, on the other hand, a shaft is made of aluminum so that its inner race to which off-load is exerted due to elastic deformation of the shaft is more susceptible to damage.
Employed as such conventional rolling bearings for automobiles are ball bearings each of which uses, for both outer and inner races, a bearing steel such as high-carbon chromium bearing steel having an oxygen content of 9 ppm or so. Standard heat treatment (so-called "whole quench hardening") has been applied to the race more susceptible to damage (i.e., the outer race in the case of an alternator or the inner race in the case of an electromagnetic clutch) to impart rolling contact fatigue strength thereto, and a grease comprising as a base oil a synthetic polyester lubricant or poly-.alpha.-olefin lubricant having a kinematic viscosity of 30-50 cSt at 40.degree. C. is filled as a lubricant.
Reflecting the technological developments in recent years, bearings to be employed in electrical components of automobiles such as alternators and electromagnetic clutches are required to meet increasingly stringent usage conditions. In particular, usage conditions for bearings to be used in alternators are becoming far more stringent, including higher temperature and speed because of higher engine performance and heavier load due to an increased belt tension. Bearings of the conventional specification, however, cannot cope with such changes in usage conditions, leading to frequent occurrence of the problem that their life is shortened due to premature flaking of the raceway surfaces of their outer races. There is accordingly an outstanding demand for the effective solution of the problem.